This laboratory found that elevated titers of serum agglutinators are present in severe suppurative infections, usually associated with Gram positive organisms. There has also been documentation of false positive and false negative reactions. Studies in progress will evaluate the influence of dysglobulinemia, malignancy, immunosuppressive drug therapy and inappropriate antibiotic therapy on these anti-Fab (IgG) antibodies. The fragmentation of IgG with subtilisin has received very little attention. Studies in progress are consequent to the observation that certain serum agglutinators disappeared almost instantaneously from a human serum after the addition of a small amount of subtilisin. It was subsequently observed that certain IgG myeloma proteins isolated or in whole serum were wholly or partially hydrolyzed while others were unaffected by the simple procedure of adding 0.1 mg subtilisin per mg total IgG and immediately examining these proteins in the ultracentrifuge. With the Department of Surgery and the Transplantation Unit, we are studying a modification of the mixed anti-globulin test for the detection of IgG antibodies directed against human kidney cells. The mixed antiglobulin test detects antibodies in the sera of patients on chronic dialysis two to four times more frequently than did either the immune adherence test or the most sensitive modification of the microlymphocytoxicity test.